Generally, a wheel pivotably mounted on a frame includes an arbor provided at both ends with pivots, each engaged in a bearing. Pivoting members formed by a bearing and a pivot are traditionally used to ensure axial and radial positioning of the rotating pieces present in the clockwork movements.
The pivot is generally made from steel and the bearing is for example made of brass, bronze, or ruby, the pairs of materials being chosen so that the frictional torque between the bearing and the pivot is as low and constant as possible.
However, pivoting members made from these pairs of materials are not always fully satisfactory regarding the value of the frictional torque and the wear obtained. They require the addition of a lubricant, inserted between the bearing and the pivot, which tends to deteriorate with time.
According to other methods described for example in documents U.S. Pat. No. 5,515,607, JP 09 211149, and DE 70 00 616, it is possible to make a wheel forming a single piece with the pivot. Such wheels comprising an integrated pivot are not the subject-matter of the present invention.
One aim of the present invention is to be able to use, in a timepiece, pivoting members whereof the contact surfaces are made from materials intrinsically having a low coefficient of friction and a low wear rate, i.e. not requiring such an addition of lubricant. This is the case in particular for bearings and pivots whereof the contact surfaces are made from diamond, another material, or a mixture of materials whereof the coefficient of friction is below 0.10. Unfortunately, such pieces are extremely difficult to manufacture using the regular machining techniques. They can for example be obtained by the method described in patent EP 1 622 826.
In particular, it is extremely difficult to product pieces as complex as a wheel arbor using the traditional methods. For example, it is extremely difficult to cut or assemble diamond pieces by riveting.
Another aim of the present invention is to propose a timepiece whereof the elements made from materials intrinsically having very low coefficients of friction and a low wear rate, i.e. not requiring the addition of lubricant, can easily be assembled.